Cook Inlet-Susitna Region Alaska Gold Production

  
Posted July 16, 2009 in Gold Mining

By A. H. KOSCHMANN and M. H. BERGENDAHL - USGS 1968

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Bounded roughly by the Aleutian or Alaska Peninsula on the southwest, the Alaska Range on the west and north, and by the Talkeetna Mountains on the east, the Cook Inlet-Susitna region includes the Kenai Peninsula, Valdez Creek, Willow Creek, and Yentna-Cache Creek mining districts.

Gold was first discovered in Alaska in 1848 in the gravels of the Kenai River. Apparently this gold was not present in minable quantities, and it was not until the 1890's that minable placers were found in the Turnagain Arm area (Martin and others, 1915, p. 181-183). The first lode deposits in the Cook Inlet-Susitna region were found in 1896 also in the Turnagain Arm area, more precisely, the Moose Pass-Hope area; however, the deposits, although rich, were of small tonnage, and there was very little lode production before 1911 (Martin and others, 1915, p. 129-131).

Placers in the Valdez Creek district, in the southern foothills of the Alaska Range, were worked from 1904 to 1924 (Ross, 1933b, p. 427-428) and desultory operations were carried on as recently as 1947 (E. H. Cobb, written commun., 1962).

In the western part of the Cook Inlet-Susitna region, placers were discovered in the Yentna-Cache Creek district in 1905 (Capps, 1913, p. 10). These deposits were moderately productive through 1957. The most productive district in the entire region is the Willow Creek district, about 20 miles north of the towns of Palmer and Wasilla, where placers were discovered in 1897. The first lode claims were located in 1906 (Capps, 1913, p. 50) and were worked fairly steadily until the early 1950's.

From 1880 through 1959, a recorded total of 919,532 ounces of gold was produced from the Cook Inlet-Susitna region. Of this, 588,361 ounces was from lode mines, 324,370 ounces from placers, and 6,801 ounces from undifferentiated sources. After the end of World War II production from both lode mines and placers declined markedly.

KENAI PENINSULA DISTRICT
The Kenai Peninsula is near the center of the southern coastline of Alaska, immediately northeast of the Alaska Peninsula.

The districts of Moose Pass-Hope, Girdwood, and Turnagain Arm—all in the central and northern part of the peninsula—have been combined in this discussion because most of their production data have been combined under "Kenai Peninsula."

Numerous small placers were discovered in the Turnagain Arm area in the early 1890's, but no significant production occurred until news of the auriferous gravels on Mills and Canyon Creeks brought several thousand prospectors to the area in 1896 (Martin and others, 1915, p. 182-183). Two years later another influx occurred. In a short time the small richer deposits were exhausted and the hand-operated rockers and sluices were supplanted by hydraulic plants that successfully mined the large reserves of low-grade gravels.

Lode mining, overshadowed by the placer operations, has been conducted chiefly in the Moose Pass-Hope camp and to a lesser degree in the Girdwood camp. The first indications of economic lode deposits were noted in 1896, but interest was diverted for a number of years to the more accessible placers. The lode deposit at the Hirshey mine, discovered in 1911, became the most consistently productive in the district (Tuck, 1933, p. 489-494). Lode mining continued sporadically until the end of World War II, when it dwindled to almost nothing.

Total recorded gold production from the Kenai Peninsula from 1895 through 1959 was 23,700 ounces from lodes, 96,500 ounces from placers, and 175 ounces from undifferentiated sources. Data from 1931 through 1945 are incomplete, so that the figures given here are minima.

The geology of the Kenai Peninsula was described by Martin and others (1915), Tuck (1933), and Park (1933). The oldest rocks on the peninsula are schists and crystalline limestones of uncertain age; however, the most widely distributed rocks are slates and graywackes that range in age from Paleozoic or Early Triassic to possible Late Cretaceous (Martin and others, 1915, p. 33-35). Granitic intrusive masses are abundant in the slaty rocks along the southern and eastern coasts. The Kenai Formation, of Eocene or younger Tertiary age, is exposed in the low country in the southwest part of the peninsula, north of Kachemak Bay, and consists of coal-bearing sand and clay. This formation is 15,000-20,000 feet thick and contains economically important oil and gas accumulations (Lian and Simonson, 1962, p. 271). Quaternary gravels— mostly till, outwash, and terrace sands and gravels —cover vast areas of lowlands in the west and northwest parts of the peninsula. The pre-Tertiary rocks that comprise most of the mountainous part of the peninsula are intricately folded whereas the Tertiary rocks, which occupy the low areas of the peninsula, are either horizontal or only gently warped into folds in which dips are generally less than 10° (Barnes and Cobb, 1959, p. 227).

The lode deposits of the Moose Pass-Hope camp consist of fissure veins. Mineralized acidic dikes are also in the district, but the gold production has been from the fissure veins that cut across the slaty cleavage of the slate and graywacke country rocks. The veins strike in all directions and have an average dip of 45° north or west (Tuck, 1933, p. 490). The ore minerals are arsenopyrite and small amounts of galena, sphalerite, pyrite, and chalco-pyrite in a gangue of quartz, calcite, and ankerite (Tuck, 1933, p. 491). Free gold occurs in the quartz, commonly near accumulations of galena and sphalerite.

The placer deposits of the Kenai Peninsula, described by Martin, Johnson, and Grant (1915, p. 181-208), are most productive in the northern part of the peninsula along the various streams— Crow, Resurrection, Palmer, Bear, and Sixmile Creeks—that debouch into Turnagain Arm. Farther south, the gravels of Canyon, Mills, Falls, and Cooper Creeks, and of the Kenai River have yielded some placer gold. The deposits were formed in Quaternary time by postglacial streams reworking and resorting the debris that choked the valleys after the retreat of the glaciers. Present streams that have incised their courses in the unconsolidated material have left terraces and have further reworked the gravels. The productive glaciers are along these streams and in channel deposits in the terraces.


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